The present invention relates to optical communications systems, and more particularly, to booster amplifiers with spectral conditioning capabilities for fiber-optic communications systems.
Fiber-optic networks are used to support voice and data communications. In optical networks that use wavelength division multiplexing, multiple wavelengths of light are used to support multiple communications channels on a single fiber.
Optical amplifiers are used in fiber-optic networks to amplify optical signals. Typical optical amplifiers are based on erbium-doped fiber coils that are pumped with diodes lasers. In-line optical amplifiers and preamplifiers are used to amplify optical data signals that have been subject to attenuation over fiber-optic links. Booster amplifiers are used to increase the optical signal power being launched into a span of transmission fiber from a transmitter module.
Transmitter modules typically contain a bank of distributed feedback lasers. Each distributed feedback laser provides light at a different wavelength. Each wavelength corresponds to a respective wavelength-division-multiplexing channel. In some systems, data may be transmitted by modulating the distributed feedback lasers directly. In other systems, data may be transmitted by using high-speed modulators to modulate the light from the distributed feedback lasers. The high-speed modulators may be part of the distributed feedback laser devices or may be external modulators such as lithium niobate waveguide modulators.
An optical multiplexer may be used to combine modulated light at different wavelengths from the distributed feedback lasers for transmission on a span of optical fiber. A booster amplifier may be used to increase the signal power of the multiplexed light before it is launched onto the span.
With this type of arrangement, it may be desirable to adjust the optical spectrum of the signals being transmitted before providing the signals to the booster amplifier.
It is therefore an object of the present invention to provide ways in which to modify the power spectrum of the channels being transmitted to a span of optical fiber in a wavelength-division-multiplexing communications link.
It is another object of the present invention to provide a booster amplifier with spectrum conditioning capabilities.
These and other objects of the invention are accomplished in accordance with the present invention by providing optical amplifier equipment for use in a fiber-optic communications link in which optical signals are transmitted on a series of spans of optical transmission fiber. Optical data signals on channels of different wavelengths may be produced by a transmitter module. A booster amplifier may be used to amplify the optical data signals. The booster amplifier may include a multiplexer that combines the signals at the different wavelengths from the transmitter module onto a single optical fiber. Optical gain stages in the booster amplifier may be used to amplify the optical signals on this fiber. The booster amplifier may include variable optical attenuators or other signal conditioning components that modify the optical spectrum of the optical data signals before the signals are transmitting over the optical communications link.